2 METHODS OF ANALYSIS [Chap. 



phoricacid; filter; add 280 grams of ammonium chlorid, 2G1 cc. of ammonium liydrox- 

 id (sp. gr. 0.90) and dilute to 2 liters. Instead of the solution of 22 grams of cal- 

 cined magnesia, 110 grams of crystallized magnesium chlorid (MgCUGIIiiO) dissolved 

 in water may be used, then add 280 grams of ammonium chlorid and proceed as above. 



(d) Dilute ammonium hydroxid for washing. — Dilute 100 cc. of ammonium hy- 

 droxid (sp. gr. 0.90) to 1 liter. 



(e) Magnesium nitrate solution. — Dissolve 320 grams of calcined magnesia in 

 nitric acid, avoiding an excess of the latter; then add a little calcined magnesia in 

 excess, boil, filter from the excess of magnesia, ferric oxid, etc., and dilute to 2 liters. 



5 PREPAJIATION OF SOLUTION. 



Treair 2 or 2.5 gi-ams of the sample by one of the methods given below: 



(a) Ignite", and di.ssolve in hydrochloric acid. 



.(b)-Evaponite.' with 5 cc. of magnesium nitrate, ignite, and dissolve in hydro- 

 chtoric aci'd; - • ' - 



(C) Boil with 20-30 cc. of strong sulphuric acid in a Kjeldahl flask, adding 2-4 

 grams of sodium or potassium nitrate at the beginning of the digestion and a small 

 quantity after the solution has become nearly colorless, or adding the nitrate in 

 small portions from time to time. After the solution is colorless add 150 cc. of water, 

 and boil for a few minutes. 



(d) Digest in a Kjeldahl flask with strong sulphuric acid and such other re- 

 agents as are used in either the plain or modified Kjeldahl or Gunning method for 

 estimating nitrogen. Do not add any potassium permanganate, but after the 

 solution has become colorless add about 100 cc. of water and boil for a few minutes. 



(e) Dissolve in 30 cc. of concentrated nitric acid and a small quantity of hydro- 

 chloric acid and boil until organic matter is destroyed. 



(f) Add 30 cc. of concentrated hydrochloric acid, heat and add cautiously, in 

 small quantities at a time, about 0.5 gram of finely pulverized potassium chlorate 

 to destroy organic matter. 



(g) Dissolve in 15-30 cc. of strong hydrochloric acid and 3-10 cc. of nitric acid. 

 This method is recommended for fertilizers containing much iron or aluminium 

 phosphate. 



After solution, cool, dilute to 200 cc. or to 250 cc. if a 2.5 gram sample was used. 

 Mix, and pour on a dry filter. 



6 DETERMINATION. 



Take an aliquot of the solution prepared as directed above, corresponding to 0.25 

 gram, 0.50 gram, or 1 gram, neutralize with ammonium hydroxid, and clear with a 

 few drops of nitric acid. In case hydrochloric or sulphuric acid has been used as 

 a solvent, add about 15 grams of dr}' ammonium nitrate or a solution containing 

 that amount. To the hot solution add 60-80 cc. of the molybdate solution for every 

 decigram of phosphoric acid (P2O5) that is present. Digest at about 65°C. for an 

 hour, and determine if the phosphoric acid has been completely precipitated by 

 the addition of more molybdate solution to the clear supernatant liquid. Fil- 

 ter and wash with cold water or, preferably, ammonium nitrate solution. Dissolve 

 the precipitate on the filter with ammonium hydroxid and hot water and wash 

 into a beaker to a bulk of not more than 100 cc. Nearly neutralize with hydrochloric 

 acid, cool, and add magnesia mixture from a burette; add slowly (about 1 drop per 

 second), stirring vigorously. After 15 minutes add 12 cc. of ammonium hydroxid 

 (sp. gr. 0.90). Let stand till the supernatant liquid is clear (2 hours is usually 

 enough) filter, wash with the dilute ammonium hydroxid until the washings are 



